This invention relates to a circuit breaker which includes cooperating stationary (fixed) and movable power contacts as well as an arrangement for blowing out the electric arc drawn during contact separation. The arrangement has a gas compressing device formed of a stationary piston and a cylinder moved by a drive rod, as well as a nozzle made of an insulating material which is affixed to the cylinder.
A gas-blast circuit breaker of the above-outlined type is conventional and is disclosed, for example, in German Laid-Open Application (Offenlegungsschrift) No. 2,363,171. In the structure described therein the movable power contact is affixed to the nozzle and the cylinder of the gas compressing device. For a circuit breaking operation, the cylinder is moved with respect to a stationary piston disposed therein, whereupon the gas contained in the cylinder is pre-compressed. A gas flow from the cylinder is generated only when the moving nozzle is no longer closed by the stationary power contact, whereupon the arc drawn between the contacts is exposed to an air blast.
It is a disadvantageous characteristic of the above construction, particularly as concerns the efficiency of the circuit breaking operation, that prior to the beginning of the gas blast, the arc burns in an environment of increased gas pressure (caused by the pre-compression) within the nozzle. As a consequence, that zone of the nozzle which plays the most important role in the subsequent extinction of the arc is heated and is soiled with soot originating from the contacts.
Further, the initially fresh blowout gas is contaminated by ionized gas within the nozzle and partially in the compression chamber as well (by virtue of backflow).
If, in a circuit breaker structure of the above-described type there is to occur a reverse gas blast into the hollow movable contact pin, it may be of advantage to close the flow path by means of an additional valve device during the compression phase, such as disclosed in German Pat. No. 2,329,501.
It is an advantage of the above-outlined structure that the gas flow path leading to the nozzle is very short.
Another type of an arc blowout circuit breaker is disclosed, for example, in German Laid-Open Application (Offenlegungsschrift) No. 2,108,871 and German Patent Application M3368 filed May 16th, 1950 and published on July 3rd, 1952. The structure disclosed therein comprises a nozzle which is made of an insulating material and which is stationary with respect to the stationary contact and the gas compressing piston. Thus, the nozzle does not move together with the movable contact. The movable contact first closes the nozzle and is, for performing the circuit breaking operation, drawn into the stationary nozzle. The gas blast starts only when the movable contact is in a fully drawn-in condition within the nozzle. The above-outlined second type of construction has the advantage that the arc first burns externally of the nozzle and then burns in the inside thereof, but with small power and in an environment of low gas pressure. As a result, substantially less combustion products are generated. Since the compression chamber in which the pre-compressed extinguishing gas is contained, is first closed off by the contact pin, the fresh gas is prevented from mixing with the ionized gas. Further, the pre-compression occurs without any gas loss. That zone of the nozzle which is of prime importance in extinguishing the arc is exposed to the arc only for a very short period. The movable contact (contact pin) opens the gas compressing chamber and allows the gas blast to begin only after the necessary extinguishing distance between the contacts is attained.
It is a disadvantage of the circuit breakers of the above-outlined second type that the gas compressing devices necessarily have a relatively long gas flow path between the compression chamber and the nozzle. Such a long flow path, because of the inherently high flow resistance, causes an undesired pressure drop. Further, the flow paths form a dead space which, in the structure disclosed in German Laid-Open Application No. 2,108,871, is additionally increased during the compression phase. Since the gas in this chamber cannot be displaced by the piston, the desirable very high compression values cannot be achieved.
It is a further disadvantage of the known circuit breaker structures that after releasing the gas blast, the compression stroke is in most cases already terminated, so that during the extinguishing phase the gas pressure drops relatively rapidly.